About 30 minutes before his show started at the RecordBar on Wednesday night, Jonathan Richman was already serenading his fans.

Sitting at a table near the bar, strumming and plucking an acoustic guitar, he sang a few songs (“Volare” was one of them) and played some instrumentals, like a busker on a street corner.

It was foreshadowing for what would follow. He and his longtime drummer, Tommy Larkins, took the stage at 10 p.m. and for more than 80 minutes they issued to a crowd of about 75 attentive and appreciative fans a heavy, warm gust of the wise and witty observations that flood his keen mind.

Richman, who will turn 64 in May, performs in a manner regularly described as childlike and eccentric. That’s true, to an extent, though the description pertains not so much to what he says as it does to how he says it: with a naivete that belies his astuteness.

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His set appeared unconventional before he’d sung a word or played a note.

The stage was equipped with no monitors, but there were three microphones: one for Larkins’ drum kit, one for Richman’s guitar and another for his vocals.

Instead of the house soundboard, he used a small, portable soundboard, which sat on stage behind him and which he fussed with throughout the show, sometimes in the middle of a song. That all contributed to the evening’s mood, which was as informal as it was impulsive and improvised.

He opened with “No One Was Like Vermeer,” a tribute to Johannes Vermeer, a Dutch painter with a mind like Richman’s: “Why are his paintings so unlike the others / Unlike the other ones so near / No one was like Vermeer.”

“That Summer Feeling” followed and it aroused the first of a few bursts of applause. It’s a sentimental ballad about the hallmarks of summer in childhood — playgrounds and fresh-cut lawns.

He improvised some lyrics, dropping in more references: kickball, bubblegum, rope swings. Next came “Because Her Beauty Was Raw and Wild,” one of several songs that displayed his deep Velvet Underground influence.

Richman has vastly remodeled “Old World,” a signature track from his days with the Modern Lovers. This version was melancholic but anti-nostalgia, issuing farewells to the pompadour, the cummerbund, mercury and lead and “James Cagney elegance.”

He also improvised lyrics to “Let Her Go Into the Darkness,” telling the ex-boyfriend he sounds like “a father, a lecturer and a busybody” when he scolds his former girlfriend for dating a drug dealer.

So it went all night. Several times, Richman stepped away from the mic and sang unamplified, pausing in the middle of songs to deliver a brief monologue or insert a ramshackle guitar instrumental.

He sang about bonfires and how one can change a party and make people “talk about sorrows they couldn’t name”; about a woman who loves “the faded colors of a 3 a.m. walk home”; about “boy thoughts” and the sex drive and when it acts “without the heart for a chaperone”; about the ego; about the sun; about Keith Richards, whose guitar “whines like a pining alley cat”; about how office cubicles make us sit still all day “when we want to play and go outside.”

He sang about love, too, about a woman who “came as an answer to a prayer” and who “loves me now more than I pray for”; and about the politics and romance and a fight he had, with regrets: “I should have been softer with her, I could have ceded more ground” and found that little voice that says “Stop, don’t say nothing.”

It was a wise piece of advice, but saying nothing hardly seems like an option for a guy who sings so sincerely and colorfully about whatever springs from his heart and mind.